Oregon Chapter
American Meteorological Society

January 1, 2010

RECORD COLD DECEMBER

By, Steve Pierce
stevejpierce@comcast.net
Executive Councilor
Oregon AMS

Headlines:
December 2009 was the coldest month in nearly 20 years at the Portland International Airport!

Summary:
Here are some of December 2009's record setting numbers, as recorded at the Portland International Airport ---

* December 2009's monthly mean temperature at the Portland International Airport (PDX) was 35.6 degrees, nearly 5 degrees below normal. This is the 4th coldest December in history at PDX, trailing only 1990, 1985 and 1978.

* December 2009 also saw the coldest stretch of overnight low temperatures in Portland Airport history, this early in the winter season, averaging 13.25 degrees from 12/8 to 12/11. This barely edges out the exact same timeframe in 1972 (12/8/72 to 12/11/72) when PDX averaged 13.75 degrees. 

* PDX recorded the single highest number of sub-freezing (32 or colder) December overnight low temperatures in nearly 25 years. There were 19 days with overnight lows at or below 32 degrees at PDX in December of 2009. The last time PDX saw more sub-freezing overnight lows in the month of December was in December 1985 when PDX recorded 25 days at or below 32 degrees.

* December 2009's mean temperature at PDX is in stark contrast to what is typical of an El Nino. Neither 1978, 1985 nor 1990 were El Nino's. 

Note - The period of record used for this analysis is 1940-2009.